It is the purpose of this project to achieve more effective treatment of human cancer through the study of tumor growth, the proliferative patterns of component tumor cells and the effects which antitumor drugs produce upon these kinetic relationships. The methylcholanthrene-induced autogenous sarcoma in the rat is the model. Detailed investigations will be made of the proliferating and non- proliferating populations during and following withdrawal of drug treatment. Drug dose levels are adjusted so as to arrest tumor growth and to be tolerated by the host. These studies are to be conducted in vivo and in vitro. Nitrogen mustard, 5 fluorouracil and adriamycin are under study and marked differences are observed in the effects of such drugs upon proliferating cells and in the replicative patterns during recovery. Additional studies deal with some control mechanisms of cell proliferation patterns and the maintenance of the complex frequency distribution of the cycle times and component intervals of the tumor cell population.